Making iso8061date.js deprecated

Fix for #605.

Several potential problems with this patch:

The JavaScript Date object doesn't retain precision beyond milliseconds and the logic uses `floor()` rather than `round()`.  For example, `2011-07-17T14:00:23.2699Z` produces 269 ms, rather than 270 ms.  I removed the round-up test as a result of this.

There was some strange goings-on in:
https://github.com/martinthomson/azure-sdk-for-node/commit/a460c3a030972ea39257a7db58b7772fedf9203e#L3L22
I've removed this, because it was fairly clear that it wasn't behaving as intended.  That might not be exactly what was intended.

I'm not 100% confident that I've tested everything.  I couldn't get the tests to pass prior to starting.  The iso8061date tests are OK, but as for the rest, I'm not sure.  Virtually none of them passed, with no good feedback.

If any of these are deal-breakers, then this is obviously not the right patch for the problem.